Method for catalytically cracking waste plastics and apparatus for catalytically cracking waste plastics

ABSTRACT

To provide a method for catalytically cracking waste plastics wherein the efficiency in decomposition is high; even polyethylene composed of linear chain molecules difficult in decomposition is decomposable at a low temperature and decomposed residue is hardly produced; the process is simple since dechlorination can be achieved at the same time with catalytically cracking waste plastics in one reaction vessel; and oil fractions can be recovered at 50% or more on a net yield basis. The method for catalytically cracking waste plastics of the present invention has a constitution in which waste plastics are loaded as a raw material into a granular FCC catalyst heated to a temperature range from 350° C. to 500° C. inside a reaction vessel, thereby decomposing and gasifying the waste plastics in contact with the FCC catalyst.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application is a continuation application of U.S. application Ser.No. 11/588,378, filed Oct. 27, 2006 (now U.S. Pat. No. 7,932,424), whichclaims the benefit of Japanese Patent Application Nos. 2006-018257,filed on Jan. 26, 2006 and 2006-203775, filed on Jul. 26, 2006 in theJapanese Intellectual Property Office, the disclosures of which areincorporated herein in their entireties by reference.

TECHNICAL FIELD

The present invention relates to a method for thermally decomposingwaste plastics, namely, waste materials of plastics such as polyethylene(PE), polypropylene (PP), polystyrene (PS) or polyethylene terephthalate(PET) and waste plastics having a resin, for example, polyvinyl chloride(PVC), in which chlorine is contained as a composition, and an apparatustherefor.

BACKGROUND OF THE INVENTION

Currently, in Japan, about 10 million tons of plastics are beingdiscarded annually as industrial waste or general waste, about 55% ofwhich are used effectively. Most of these waste plastics are used asfuels for generating electricity or other heat sources, and notsubstantially recycled as chemical materials. An unused portion of thesewaste plastics is disposed of in landfills or subjected to incinerationdisposal. However, available landfills are becoming tighter year by yearand there is a fear of generating dioxins on incineration when resinsare mixed such as polyvinyl chloride (PVC) containing a chlorine-basedcomposition.

Under these circumstances, such technology development is ardentlydesired that waste plastics be subjected to thermal decomposition toobtain a petroleum resource such as fuel oil. More specifically, wasteplastics are subjected to thermal decomposition and utilized as apetroleum resource. The thus obtained petroleum resource is used asgasoline, kerosene, light oil or heavy oil. Alternatively, wasteplastics are subjected to thermal decomposition to obtain an oilfraction. The oil fraction is further separated into a naphtha fractionwhich is then used as a raw material for producing chemicals. Varioustechnologies are known by which waste plastics are thermally decomposedto obtain oil fractions as described above.

As technology in which waste plastics having a mixture of resincontaining chlorine as a composition, for example, polyvinyl chloride(PVC), are thermally decomposed to obtain an oil fraction, PatentDocument 1 has disclosed a method for thermally decomposing wasteplastics to petroleum, including a first thermal decomposition step inwhich high-temperature sands (600° C. to 950° C.) are added to wasteplastics and heated to a temperature range from 250° C. to 350° C. toseparate chlorine, a second thermal decomposition step in which wasteplastics from which the chlorine content is removed are further heatedto a higher temperature range (350° C. to 500° C.) with high-temperaturesands (600° C. to 950° C.) to effect thermal decomposition, and ancombustion step in which gaseous combustible substances formed at thefirst thermal decomposition step and decomposed residue formed at thesecond thermal decomposition step is subjected to combustion, wherein atthe first thermal decomposition step the waste plastics are brought intocontact with fine particles of a neutralizing agent (hydrated lime andthe like), a separated chlorine content is coupled to the neutralizingagent, and at least a part of the neutralizing agent coupled to thechlorine content is led to the combustion step together with gaseouscombustible substances formed at the first thermal decomposition step.In this conventional technology, FCC waste catalysts are also added to athermal decomposition area at the second thermal decomposition step at 5weight % to 35 weight % with respect to waste plastics.

-   Patent Document 1: Japanese Published Unexamined Patent Application    No. 2001-107058

SUMMARY OF THE INVENTION

However, the above-described conventional technology has the followingproblems.

(1) The conventional technology is carried out on the basis of a firstthermal decomposition step in which high-temperature sands are added towaste plastics to separate chlorine content and a second thermaldecomposition step in which waste plastics from which chlorine contentis removed are further heated by using sands as a fluid vehicle to ahigher temperature, thereby causing thermal decomposition. Namely, sincethe technology is a multiple stage process in which sands are used as afluid vehicle in all the steps, an apparatus is complicated in structureto raise the processing cost, which is a problem. The efficiency ofdecomposition reaction is poor, and net yield of oil fractions is low indecomposing cracked gas to petroleum, which is also a problem.

(2) Hydrogen chloride is carried over from a dechlorination step ofwaste plastics to a thermal decomposition step, chlorine is left asorganic chlorine content at 1000 ppm or more with respect to the thusobtained oil fraction, which is a problem.

(3) Polyethylene (PE) must be heated up to a high temperature (440° C.to 450° C.) on thermal decomposition, and it may easily causecarbonization when mixed with high-temperature sands, thereby generatinga great amount of decomposed residue, which is also a problem.

The present invention solves the above-described conventional problems,an object of which is to provide a method for catalytically crackingwaste plastics, which is excellent in decomposition reaction efficiency,capable of decomposing polyethylene composed of linear chain moleculesdifficult in decomposition, at a low temperature, with a negligiblequantity of decomposed residue, simple in process and able to realize ahigh energy efficiency of 50% or more in terms of net yield of oilfraction, and a catalytically cracking apparatus.

In order to solve the above problems, a method for catalyticallycracking waste plastics and an apparatus for catalytically crackingwaste plastics according to the present invention are constituted asfollows.

The method for catalytically cracking waste plastics according to afirst aspect of the present invention is constituted so that wasteplastics are loaded as a raw material into a granular FCC catalystheated to a temperature range from 350° C. to 500° C. inside a reactionvessel, thereby the waste plastics in contact with the FCC catalyst aredecomposed and gasified.

The following actions are obtained due to the above-describedconstitution.

(1) Granular FCC catalyst is used as a thermal vehicle and wasteplastics (a raw material) are loaded into the preliminarily heated FCCcatalyst inside the reaction vessel, by which the granular FCC catalystis brought into contact with the waste plastics to facilitate the heattransfer and reaction and catalytically crack the waste plastics atshort times. Therefore, even polyethylene composed of linear chainmolecules difficult in decomposition is decomposable at a lowtemperature, and decomposed residue is hardly produced, withcarbonization kept to a negligible level.

(2) Since a granular FCC catalyst large in specific surface area is usedas a thermal vehicle to facilitate the heat transfer and reactionthrough contact with waste plastics in one reaction vessel, the processis simple and the energy efficiency is high.

In this instance, the waste plastics are waste mainly containingplastics which are separated from urban wastes and industrial waste andbased on thermoplastic resins such as polyethylene, polypropylene,polystyrene and polyethylene terephthalate. They may contain polyvinylchloride (PVC) including chlorine as a composition or foreignsubstances, such as thermosetting plastic, FRP, paper. Reinforced fiberof FRP may be discharged out of the reaction vessel regularly asdecomposed residue.

It is preferable to use waste plastics which are broken down into smallpieces such as beads, flakes, chips, granules or pellets in view of anincrease in catalytically cracking efficiency. Large waste plasticsformed in a mass may be subjected to decomposition and subsequentprocesses but not desirable due to a longer time required for theprocesses.

The FCC catalyst used is a solid acid catalyst based on syntheticzeolite which is granulated into granular particles of 40 to 80 μm usedin the FCC (fluid catalyst cracking) process of petroleum. Since the FCCcatalyst is substantially similar to waste plastics in mean specificgravity of 0.74 to 0.91,

it can be mixed well with waste plastics inside a reaction vessel.Off-specification catalysts discharged from catalyst manufacturers andwaste catalysts discharged from petroleum refinery plants may also beused. A mixture of these catalysts may also be used.

The waste catalyst is called FCC (U) (fluid catalyst cracking (used))and obtained by regenerating catalysts used in fluid catalytic crackingfor selectively catalytically cracking a wide variety of petroleumfractions covering light oil to normal pressure residue. It is alsocalled an equivalent catalyst or regenerated catalyst. In petroleumrefining plants, the catalyst is recycled between a catalytic crackingarea and a regeneration area. A new catalyst is constantly supplied in apredetermined quantity to offset catalytic deterioration. A quantity ofthe catalyst corresponding to the thus supplied quantity is dischargedoutside a system. Waste catalysts discharged outside the system arerecycled inside the system and still have a sufficient catalyticactivity. More specifically, catalysts used in refining crude oil aretaken out in a state where coke and others are still mixed, sent to aregeneration tower after steam stripping of associated hydrocarbons,into which air is blown, thereby burning the coke to activate thecatalysts. For example, the FCC catalyst obtained at refinery plants andothers is 0.74 to 0.91 in mean specific gravity, which is substantiallyequal to that of waste plastics, and can be mixed well inside a reactionvessel. It is from 61 to 75 μm in mean particle size and quite low incost, as compared with a new catalyst. Further, the FCC catalyst is asynthetic zeolite mainly based on SiO2 and Al2O3, and catalysts in whichNa, Fe, C, V, Ni, Sb and others are mixed in a small quantity arecommonly used.

FCC catalysts and waste plastics inside a reaction vessel are mixed bymeans of agitation, and the like, by the which waste plastics arebrought into contact with the FCC catalyst to cause decomposition andgasification of the waste plastics.

The FCC catalyst inside the reaction vessel should be heated in a rangefrom 350° C. to 500° C., preferably from 400° C. to 480° C. and morepreferably from 410° C. to 430° C. As the heating temperature decreasesto 410° C. or lower, wax content in oil fractions decreases accordinglybut such a tendency is found that decomposition occurs for a longertime. As the temperature increases to 430° C. or higher, thedecomposition can be shortened but there is a tendency that the waxcontent in oil fractions increases. As the temperature decreases to 400°C. or lower, in addition to the above-described tendencies, such atendency is also found that decomposed residue increases. Further, asthe temperature decreases to 350° C. or lower, this tendency is moreconspicuous, which is not desirable. As the temperature increases to480° C. or higher, in addition to the tendencies so far described, wasteplastics are carbonized easily and there is a tendency that decomposedresidue increases. As the temperature increases to 500° C. or higher,this tendency is conspicuous, which is not desirable.

The FCC catalyst is preferably used in a quantity corresponding to 20 to60 vol % of the capacity of a reaction vessel. When a quantity of theFCC catalyst is lower than 20 vol % of the capacity of the reactionvessel, waste plastics are in contact with the FCC catalyst in a smallerquantity, resulting in a longer decomposition and processing time and alower processing efficiency. Where a quantity of the FCC catalyst islarger than 60 vol % or more, the FCC catalyst and decomposed residuemust be discharged frequently, thereby making the operation troublesome,which is not desirable. This is due to the fact that when waste plasticsare loaded into the reaction vessel one after another, decomposedresidue resulting from the waste plastics (carbon of paper labels andplastics or metals adhered to waste plastics and others) areaccumulated, the reaction vessel is filled with the FCC catalyst and thedecomposed residue, restricting a quantity of the waste plastics loadedinto the reaction vessel, and the FCC catalyst and the decomposedresidue must be frequently discharged for loading the waste plasticsconstantly.

When the FCC catalyst is used, waste plastics, for example, polyethylene(PE) will undergo decomposition by ion reaction. The FCC catalyst iszeolite, namely, an acid catalyst. In decomposition of waste plastics,at first, this acid catalyst supplies protons to carbon, therebygenerating pentacoordinate carbon. Since the pentacoordinate carbon isunstable, it releases hydrogen to be a carbenium ion. The carbenium ionis in an equilibrium state that ion-sharing intermediates are found.Most of the carbenium ions are structured to undergo skeletalisomerization due to a higher stability of the structure. Since acarbenium ion is also liable to break down at the linkage of betaposition, it is decomposed into an i-paraffin and carbenium ion. Thiscarbenium ion repeats decomposition through isomerization and formationof intermediates. Further, when H⁻ is obtained in a state of a carbeniumion, it is not decomposed but kept isomerized in the structure.

In contrast, where a carbenium ion contains many double bonds, it isformed into a hexagonal intermediate and aromatized. A linear-chaincarbenium ion is decomposed to have olefin and H⁻ and then formed into aparaffin. Therefore, the products are mostly branched and it isconsidered that the products become diversified. This finding is also inagreement with the results of Examples. Further, a larger content ofbranched and aromatized products may frequently cause a sterichindrance, resulting in a poor crystallization and a decreased contentof wax. Further, since reactions for generating a carbenium ion takeplace at a lower temperature than radical chain reactions, a carbeniumion is easily decomposable to facilitate the reactions, by which the ionmay be formed into lower molecular weight products. As a result, the useof the FCC catalyst (FCC(U)) makes it possible to decompose polyethylene(PE) at a low temperature, thereby eliminating problems of carbonizationand wax conversion and successfully providing a high-quality crackedoil.

Further, waste plastics are preferably subjected to catalyticallycracking under a normal pressure. This is because waste plastics may behardly evaporated and easily carbonized on application of pressure.However, in order to prevent carbonization of waste plastics, thepressure inside a reaction vessel may be reduced to catalytically crackwaste plastics at a low temperature.

The present invention is a method for catalytically cracking wasteplastics discussed above, which is constituted so that cracked gasgenerated by decomposition and gasification of the waste plastics iscooled to obtain oil fractions.

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) Waste plastics are facilitated for heat transfer and reaction,subjected to catalytically cracking, and then cooled to obtain oilfractions. Therefore, even polyethylene (PE) difficult in decompositionis decomposable at a low temperature to obtain oil fractions at a highyield of 90%. The oil fractions can be recovered at 50% or more on a netyield basis, thereby attaining a high energy efficiency.

(2) Since even polyethylene composed of linear chain molecules isdecomposable at a low temperature, wax is less likely to be produced,thereby providing oil fractions lower in flow-point (0° C. or lower).

In this instance, a rare gas such as argon or an inert gas such asnitrogen is introduced as a carrier gas into a reaction vessel, by whichcracked gas generated inside the reaction vessel can be taken out fromthe reaction vessel, together with the carrier gas.

The present invention is a method for catalytically cracking wasteplastics discussed above, which is constituted so that granular Cacompounds are mixed with the FCC catalyst.

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) In decomposing to petroleum waste plastics having resins, such asPVC, in which chlorine atoms are contained, no independentdechlorination step is needed, and hydrogen chloride generated by adechlorination reaction is also removed instantly by reaction with Cacompounds, thereby making it possible to obtain oil fractions extremelylow in chlorine concentration. In other words, organic chlorine is stillfound at 1000 ppm when the thermal decomposition is conducted accordingto a conventional technology, while it is found only at a decreasedcontent of 100 ppm according to the present invention.

(2) Since hydrogen chloride generated by a dechlorination reactionreacts with Ca compounds inside a reaction vessel and is fixed into theCa compounds, it is possible to prevent corrosion or others resultingfrom hydrogen chloride.

In this instance, Ca(OH)₂, CaCO₃, CaO and the like are used as Cacompounds. Chlorine removed from waste plastics inside a reaction vesselis formed as hydrogen chloride. Ca compounds react with hydrogenchloride to form Ca chlorides, and hydrogen chloride is trapped byCa(OH)₂, CaCO₃ and CaO according to the respective chemical reactionsshown below.CaO+2HCl→CaCl₂+H₂OCaCO₃+2HCl→CaCl₂+H₂O+CO₂Ca(OH)₂+2HCl→CaCl₂+2H₂O  [Chemical formula 1]

Ca compounds are mixed preferably at 15 to 50 parts by mass with respectto 100 parts by mass of the FCC catalyst. When Ca compounds are mixed at15 parts by mass or less, hydrogen chloride which is not trapped isincreased accordingly, although depending on a ratio of mixed resinscontaining chlorine atoms, thereby corroding a reaction vessel andothers more frequently and resulting in a tendency that chlorineconcentration in oil fractions is increased. When Ca compounds are mixedat 50 parts by mass or more, such a tendency is found that the run-offspeed is slow in decomposition reaction of plastics and the yield islowered, which is not desirable.

Further, Ca compounds are preferably mixed at 50 to 200 mol % withrespect to a mass of resins containing chlorine atoms such as PVC. WhenCa compounds are mixed at 50 mol % or less, hydrogen chloride which isnot trapped is increased accordingly, and such a tendency is found thata reaction vessel and others are easily corroded. When they are mixed at200 mol % or more, such a tendency is found that the run-off speed isslow in decomposition reaction of plastics and the yield is lowered,which is not desirable either.

Hydrogen chloride reacts with Ca compounds to form calcium chloride.This calcium chloride has found many applications such as ananti-freezing agent for roads, a dust control agent for roads andconstruction sites and food additive and can be used effectively.

The FCC catalyst and others remaining inside a reaction vessel after thedecomposition reaction of waste plastics are washed to dissolvewater-soluble calcium chloride in water, by which they are dischargedoutside the reaction vessel, and the FCC catalyst and unreacted Cacompounds difficult to dissolve in water may be allowed to remain insidethe reaction vessel. The FCC catalyst and Ca compounds remaining insidethe reaction vessel are regenerated after being dried inside thereaction vessel, and supplemented with Ca compounds for subsequentreuse. Calcium chloride in drainage after the FCC catalyst and the likeare washed is determined for concentration to calculate a quantity of Cacompounds used in a dechlorination reaction, and then Ca compounds maybe supplemented in the thus calculated quantity.

The present invention is a method for catalytically cracking wasteplastics discussed above, which is constituted so that granular ironcompounds are mixed with the FCC catalyst.

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) Besides the FCC catalyst and Ca compounds, iron compounds are addedand allowed to exist inside a reaction vessel, thereby attaining aremarkable improvement in the dechlorination rate and providing oilfractions extremely low in chlorine content of no more than 100 ppm, forexample, 85 ppm.

(2) Addition of iron compounds makes it possible to prevent catalystpoisoning resulting from chlorine and extend the life of the FCCcatalyst about 3 times, thereby providing a long-life FCC catalyst.

In this instance, iron oxides such as Fe₂O₃, iron hydroxide (III)(FeO(OH)) and substances containing iron hydroxide (III) such as ironore are used as iron compounds.

Iron compounds are preferably mixed at 5 to 50 mass % with respect tothe FCC catalyst. When the iron compounds are mixed at 5 mass % or lesswith respect to the FCC catalyst, such a tendency is found thatdechlorination is decreased accordingly. When they are mixed at 50 mass% or more, such a tendency is found that waste plastics are brought intocontact with the FCC catalyst less efficiently and the decompositionefficiency of the waste plastics is decreased accordingly, which is notdesirable.

The present invention is a method for catalytically cracking wasteplastics discussed above, which is constituted so that the ironcompounds contain iron hydroxide (III) (FeO(OH)).

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) Besides the FCC catalyst and Ca compounds, iron hydroxide (III) andothers are added and allowed to exist inside a reaction vessel, therebyattaining a further improvement in the dechlorination rate and providingoil fractions extremely low in chlorine content of no more than 100 ppm,for example, 74 ppm.

In this instance, iron hydroxide (III) (FeO(OH)) and iron ore may beused as iron compounds containing iron hydroxide (III) (FeO(OH)).

The present invention is a method for catalytically cracking wasteplastics discussed above, which is constituted so that the wasteplastics are subjected to decomposition and gasification in anatmosphere where an inert gas is introduced into the reaction vessel.

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) Waste plastics are subjected to decomposition and gasification in anatmosphere where an inert gas is introduced into a reaction vessel andthe waste plastics are heated and decomposed inside the reaction vesselpurged by the inert gas or scarce in oxygen, thereby making it possibleto prevent generation of dioxins and contributing to the environmentalprotection.

In this instance, a rare gas such as argon, nitrogen and carbon dioxidemay be used as an inert gas.

The flow rate of inert gas introduced into a reaction vessel and theconcentration of inert gas inside the reaction vessel are appropriatelyestablished depending on the size of the reaction vessel and a quantityof waste plastics.

The present invention is a method for catalytically cracking wasteplastics discussed above, in which the reaction vessel is a rotarykiln-type reaction vessel and which is constituted so that at least theFCC catalyst is loaded and agitated continuously to effect decompositionand gasification.

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) The reaction vessel is a rotary kiln-type reaction vessel and thewaste plastics are loaded continuously, agitated by rolling motion, andbrought into contact with the FCC catalyst to effect decomposition andgasification. Thus, the operation can be conducted continuously toattain a remarkable improvement in productivity.

In this instance, since a heated FCC catalyst is available inside areaction vessel, at least, waste plastics are loaded continuously,thereby making it possible to decompose and gasify the waste plastics.Ca compounds or iron compounds may be mixed in advance with the FCCcatalyst inside the reaction vessel to load the waste plastics into thereaction vessel. Further, the Ca compounds, iron compounds and FCCcatalyst may be loaded into the reaction vessel, together with the wasteplastics.

After continuous operation for a predetermined time, the FCC catalyst,Ca compounds or iron compounds before or after reaction and decomposedresidue of waste plastics remaining inside the reaction vessel areremoved, and the FCC catalyst, Ca compounds and iron compounds areseparated from the decomposed residue of the waste plastics by using asieve or the like and taken out separately. Further, washing or the likeis conducted to dissolve Ca compounds (calcium chloride) after reactionwith hydrogen chloride, thereby making it possible to take out the Cacompounds, iron compounds and FCC catalyst before reaction.

The present invention is a method for manufacturing waste plasticsdiscussed above, which is constituted to use a waste catalyst as the FCCcatalyst.

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) Where a waste catalyst is used as the FCC catalyst, waste catalysts(industrial waste), the treatment of which poses a problem, can beutilized effectively. Further, since they are quite low in cost ascompared with a new catalyst, waste plastics can be subjected todecomposition at a low cost.

The apparatus for catalytically cracking waste plastics of the presentinvention is constituted to have a reaction vessel provided with aheating means for heating a granular FCC catalyst to a temperature rangefrom 350° C. to 500° C. and an agitating means for mixing and agitatingthe FCC catalyst with waste plastics as a raw material.

The following actions are obtained due to the above-describedconstitution.

(1) Granular FCC catalyst is used as a thermal vehicle, waste plastics(a raw material) are loaded into the preliminarily heated FCC catalystinside a reaction vessel, by which the granular FCC catalyst and thewaste plastics are mixed and agitated to facilitate the heat transferand reaction and the waste plastics are catalytically cracked at shorttimes. Therefore, the apparatus is made simple in structure, evenpolyethylene composed of linear chain molecules difficult indecomposition is decomposable at a low temperature, carbonization isless likely to take place and decomposed residue is hardly produced.

(2) Granular FCC catalyst larger in specific surface area is used as athermal vehicle, and waste plastics are brought into contact therewithin one reaction vessel to facilitate the heat transfer and reaction.Therefore, the process is simple and the energy efficiency is high.

In this instance, there is no particular restriction on a heating means,as long as it is able to heat a reaction vessel to a temperature from350° C. to 500° C. For example, a heating means is used by which thereaction vessel is heated by radiation heat outside or inside thereaction vessel. Another heating means is available by which hot air isblown into a reaction vessel to heat the inner part of the reactionvessel. Further, an electric heater or the like may be used to heat thereaction vessel.

An agitating vane installed inside a reaction vessel may be used as anagitating means. Further, where the reaction vessel is a rotationalcylinder, the FCC catalyst can be agitated by the rolling motion withoutusing an agitating vane. Still further, an agitating media such as ballsare placed into the reaction vessel. In addition, a reaction vessel isgiven as a tilted rotational cylinder, by which waste plastics loadedinto the reaction vessel are moved axially by the rolling motion toeffect agitation.

Since an explanation has been made for the FCC catalyst above, wasteplastics and heating temperature above, they will not be explained here.

It is preferable that the apparatus for catalytically cracking wasteplastics is provided with a loading apparatus which loads FCC catalystmixed with Ca compounds inside the reaction vessel.

The following actions are obtained due to the above-describedconstitution.

(1) In catalytically decomposing to petroleum waste plastics havingresins, such as PVC, in which chlorine atoms are contained, noindependent dechlorination mechanism is needed. Further, hydrogenchloride generated by a dechlorination reaction is removed instantly byreaction with Ca compounds, thereby making it possible to obtain oilfractions extremely low in chlorine concentration. In other words,organic chlorine is still found at 1000 ppm when the thermaldecomposition is conducted according to a conventional technology, whileit is found only at a decreased content of 100 ppm according to thepresent invention.

(2) Since hydrogen chloride generated by a dechlorination reactionreacts with Ca compounds inside a reaction vessel and is fixed into theCa compounds, it is possible to prevent corrosion or others resulting ofthe reaction vessel, a cracked gas pipe and others from hydrogenchloride.

The Ca compounds have been described above, the explanation of whichwill be omitted here.

The loading apparatus can be used as the loading apparatus for rawmaterial which loads waste plastics into the reaction vessel. Conveyerand others can be used as the loading apparatus.

The following action can be obtained due to mixing granular ironcompounds into FCC catalyst.

(1) Besides the FCC catalyst and Ca compounds, iron compounds are addedand allowed to exist inside a reaction vessel, thereby attaining aremarkable improvement in the dechlorination rate and providing oilfractions extremely low in chlorine concentration of no more than 100ppm, for example, 85 ppm.

(2) Addition of iron compounds makes it possible to prevent catalystpoisoning resulting from chlorine and extend the life of the FCCcatalyst about 3 times, thereby providing a long-life FCC catalyst.

The iron compounds have been described above, the explanation of whichwill be omitted here.

Also it is preferable that the apparatus for catalytically crackingwaste plastics is provided with a discharge mechanism for discharging atleast the FCC catalyst outside the reaction vessel.

The following actions are obtained due to the above-describedconstitution.

(1) Since the apparatus is provided with a discharge mechanism fordischarging the FCC catalyst outside a reaction vessel, the FCC catalystor decomposed residue and the like inside the reaction vessel aredischarged outside the reaction vessel after the catalytically crackingof waste plastics, by which the FCC catalyst inside the reaction vesselis adjusted to an appropriate quantity so that the waste plastics can beloaded. When waste plastics are loaded into a reaction vessel one afteranother, the reaction vessel is filled with the FCC catalyst anddecomposed residue, thereby restricting a quantity of the waste plasticswhich can be loaded into the reaction vessel.

A screw conveyer and the like may be used as the discharge mechanism.The FCC catalyst, decomposed residue of waste plastics, or Ca compoundsand iron compounds before or after reaction inside a reaction vessel canbe discharged regularly from a discharge port formed at a predeterminedsite such as a lower part of the reaction vessel outside the reactionvessel by using the discharge mechanism such as a screw conveyor.

The discharged FCC catalyst and the like are separated from decomposedresidue on the basis of a difference in specific gravity or by using asieve and remaining portions are washed, thereby dissolvingwater-soluble calcium chloride in water to take out the FCC catalyst, Cacompounds and iron compounds prior to reaction. The thus taken out FCCcatalyst, Ca compounds and iron compounds are regenerated, whenevernecessary, after being dried. They can be, then, reused by supplementingCa compounds. The concentration of calcium chloride in drain water afterthe FCC catalyst is washed is determined to calculate a quantity of Cacompounds used in a dechlorination reaction, and the thus calculatedquantity may be supplemented accordingly.

When waste plastics are subjected to a repeated catalytic crackinginside a reaction vessel, decomposed residue accumulates inside thereaction vessel, and carbon attached to the surface of the FCC catalystdeactivates the FCC catalyst, thereby decreasing the decompositionperformance. The deactivated FCC catalyst can be regenerated by heatingunder an oxygen atmosphere inside the reaction vessel to burn off theattached carbon. It is preferable to give an oxygen concentration of 1to 20% and a heating temperature of 500 to 650° C. inside the reactionvessel. Further, it is preferable to give a heating time of 2 to 12hours, depending on the heating temperature.

When the reaction vessel is heated under the above-described conditions,it is possible to burn off decomposed residue accumulated inside thereaction vessel and regenerate the FCC catalyst, without discharging theFCC catalyst or decomposed residue from the reaction vessel. The FCCcatalyst can be regenerated inside the reaction vessel, by which wasteplastics are subjected to a prolonged decomposition and gasification,without a separate mechanism for regenerating the FCC catalyst.

The present invention is the apparatus for catalytically cracking wasteplastics discussed above, which is provided with a cooling mechanism forcooling and liquefying cracked gas generated by decomposition of thewaste plastics.

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) Waste plastics are facilitated for heat transfer and reaction,subjected to catalytically cracking and then cooled to obtain oilfractions. Therefore, even polyethylene (PE) difficult in decompositionis decomposable at a low temperature to obtain oil fractions at a highyield of 90%. The oil fractions can be recovered at 50% or more on a netyield basis, thereby attaining a high energy efficiency.

(2) Since even polyethylene composed of linear chain molecules isdecomposable at a low temperature, wax is less likely to be produced,thereby providing oil fractions lower in flow-point (0° C. or lower).

In this instance, there is no particular restriction on a cooling meansas long as it is able to cool cracked gas to a point lower than the dewpoint and liquefy it.

The present invention is the apparatus for catalytically cracking wasteplastics discussed above, which is constituted so that the reactionvessel is a rotary kiln-type reaction vessel.

The following actions are obtained due to the above-describedconstitution, in addition to the action discussed above.

(1) The reaction vessel is the rotary kiln-type reaction vessel andwaste plastics are loaded continuously, agitated by rolling motion, andbrought into contact with the FCC catalyst to effect decomposition andgasification. Thus, the operation can be conducted continuously with asimple apparatus to attain a remarkable improvement in productivity.

As described so far, the following favorable effects can be obtained bya method for catalytically cracking waste plastics and an apparatus forcatalytically cracking waste plastics according to the presentinvention.

According to the present invention,

(1) a method for catalytically cracking waste plastics can be providedin which even polyethylene composed of linear chain molecules difficultin decomposition is decomposable at a low temperature and decomposedresidue is hardly produced, with carbonization kept to a negligiblelevel, since the granular FCC catalyst is used as a thermal vehicle,waste plastics (a raw material) are loaded into the high-temperature FCCcatalyst inside a reaction vessel, the granular FCC catalyst is broughtinto contact with the waste plastics to facilitate the heat transfer andreaction, thereby catalytically cracking the waste plastics, and

(2) a method for catalytically cracking waste plastics can be providedwhich is simple in process and high in energy efficiency, since thegranular FCC catalyst large in specific surface area is used as athermal vehicle to facilitate the heat transfer and reaction throughcontact with waste plastics.

According to the present invention, in addition to the effect discussedabove,

(1) a method for catalytically cracking waste plastics can be providedin which even polyethylene (PE) difficult in decomposition isdecomposable at a low temperature to obtain oil fractions at a highyield of 90% and the oil fractions can be recovered at 50% or more on anet yield basis, thereby attaining a high energy efficiency, since wasteplastics are facilitated for heat transfer and reaction, subjected tocatalytically cracking and then cooled to obtain oil fractions, and

(2) a method for catalytically cracking waste plastics can be providedin which wax is less likely to be produced, thereby providing oilfractions lower in flow-point (0° C. or lower), since even polyethylenecomposed of linear chain molecules is decomposable at a low temperature.

According to the present invention, in addition to the effect discussedabove,

(1) a method for catalytically cracking waste plastics can be providedin which oil fractions extremely low in chlorine concentration of 100ppm can be obtained, since in catalytically cracking to petroleum wasteplastics having resins, such as PVC, in which chlorine atoms arecontained, no independent dechlorination step is needed and hydrogenchloride generated by a dechlorination reaction is also removedinstantly by reaction with Ca compounds, and

(2) a method for catalytically cracking waste plastics can be providedin which corrosion or others resulting from hydrogen chloride areprevented, since hydrogen chloride generated by a dechlorinationreaction reacts with Ca compounds inside a reaction vessel and is fixedinto the Ca compounds.

According to the present invention, in addition to the effect discussedabove,

(1) a method for catalytically cracking waste plastics can be providedin which besides the FCC catalyst and Ca compounds, iron compounds areadded and allowed to exist inside a reaction vessel, thereby attaining aremarkable improvement in dechlorination rate and providing oilfractions extremely low in chlorine concentration of no more than 100ppm, for example, 85 ppm, and

(2) a method for catalytically cracking waste plastics can be providedin which addition of iron compounds enables to extend the life of theFCC catalyst about 3 times, thereby providing a long-life FCC catalyst.

According to the present invention, in addition to the effect discussedabove,

(1) a method for catalytically cracking waste plastics can be providedin which besides the FCC catalyst and Ca compounds, iron hydroxide (III)and others are added and allowed to exist inside a reaction vessel,thereby attaining a further improvement in the dechlorination rate andproviding oil fractions extremely low in chlorine concentration of nomore than 100 ppm, for example, 74 ppm.

According to the present invention, in addition to the effect discussedabove,

(1) waste plastics are subjected to decomposition and gasification in anatmosphere in which an inert gas is introduced into a reaction vesseland they are heated and decomposed in a state that the reaction vesselis purged inside by the inert gas or oxygen is scarce, thereby making itpossible to prevent generation of dioxins and contributing to theenvironmental protection.

According to the present invention, in addition to the effect describedabove,

(1) a method for catalytically cracking waste plastics can be providedin which the operation can be conducted continuously to attain aremarkable improvement in productivity, since the reaction vessel is arotary kiln-type reaction vessel and waste plastics are loadedcontinuously, agitated by rolling motion, and brought into contact withthe FCC catalyst to effect decomposition and gasification.

According to the present invention, in addition to the effect discussedabove,

(1) Waste catalysts (industrial waste), the treatment of which poses aproblem, can be utilized effectively. Further, since waste catalysts arequite low in cost as compared with a new catalyst, a method forcatalytically cracking waste plastics is provided in which wasteplastics can be subjected to decomposition at a low cost.

According to the present invention,

(1) an apparatus for catalytically cracking waste plastics can beprovided in which the structure is simplified, even polyethylenecomposed of linear chain molecules difficult in decomposition isdecomposable at a low temperature, and decomposed residue is hardlyproduced, with carbonization kept to a negligible level, since thegranular FCC catalyst is used as a thermal vehicle and waste plastics (araw material) are loaded into the high-temperature FCC catalyst inside areaction vessel, the granular FCC catalyst and the waste plastics aremixed and agitated to facilitate the heat transfer and reaction andcatalytically cracking the waste plastics, and

(2) an apparatus for catalytically cracking waste plastics can beprovided which is simple in process and high in energy efficiency, sincethe granular FCC catalyst large in specific surface area is used as athermal vehicle to facilitate the heat transfer and reaction throughcontact with waste plastics.

According to the present invention, in addition to the effect discussedabove,

(1) an apparatus for catalytically cracking waste plastics can beprovided in which even polyethylene (PE) difficult in decomposition isdecomposable at a low temperature to obtain oil fractions at a highyield of 90%, and the oil fractions can be recovered at 50% or more on anet yield basis, thereby attaining a high energy efficiency, since wasteplastics are facilitated for heat transfer and reaction, subjected tocatalytically cracking, and then cooled to obtain oil fractions, and

(2) an apparatus for catalytically cracking waste plastics can beprovided in which wax is less likely to be produced, thereby providingoil fractions lower in flow-point (0° C. or lower), since evenpolyethylene composed of linear chain molecules is decomposable at a lowtemperature.

According to the present invention, in addition to the effect discussedabove,

(1) an apparatus for catalytically cracking waste plastics can beprovided in which the operation can be conducted continuously with asimple apparatus to attain a remarkable improvement in productivity,since the reaction vessel is a rotary kiln-type reaction vessel andwaste plastics are loaded continuously, agitated by rolling motion, andbrought into contact with the FCC catalyst to effect decomposition andgasification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a method for catalyticallycracking waste plastics and the apparatus therefore (reaction process)according to one example of the present invention.

FIG. 2 is a graph illustrating a relationship between the oil fractionefflux time and the cumulative run-off quantity (weight %) in a methodfor catalytically cracking waste plastics according to one example ofthe present invention.

FIG. 3 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics according to oneexample of the present invention.

FIG. 4 is a graph illustrating a relationship between the oil fractionefflux time and the cumulative run-off quantity (weight %) in a methodfor catalytically cracking waste plastics (the reaction temperature ischanged at three different levels) according to another example ofpresent invention.

FIG. 5 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics (the reactiontemperature is changed at three different levels) according to anotherexample of the present invention.

FIG. 6 is a graph illustrating a change in gas production in a methodfor catalytically cracking waste plastics (the reaction temperature ischanged at three different levels) according to another example of thepresent invention.

FIG. 7 is a graph illustrating a relationship between the oil fractionefflux time and the cumulative run-off quantity (weight %) in a methodfor catalytically cracking waste plastics (FCC waste catalyst (FCC(U))is used at three different quantity levels) according to another exampleof the present invention.

FIG. 8 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics (FCC wastecatalyst (FCC(U)) is used at three different quantity levels) accordingto another example of the present invention.

FIG. 9 is a graph illustrating a change in gas production in a methodfor catalytically cracking waste plastics (FCC waste catalyst (FCC(U))is used at three different quantity levels) according to another exampleof the present invention.

FIG. 10 is a graph illustrating a relationship between the oil fractionefflux time and the cumulative run-off quantity (weight %) in a methodfor catalytically cracking waste plastics (the raw material is changedto each of PE, PP and PS) according to another example of the presentinvention.

FIG. 11 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics (the raw materialis changed to each of PE, PP and PS) according to another example of thepresent invention.

FIG. 12 is a graph illustrating a change in gas production in a methodfor catalytically cracking waste plastics (the raw material is changedto each of PE, PP and PS) according to another example of the presentinvention.

FIG. 13 is a graph illustrating a relationship between the oil fractionefflux time and the cumulative run-off quantity (weight %) in a methodfor catalytically cracking waste plastics (the raw material used is amixture of PE, PP and PS) according to another example of the presentinvention.

FIG. 14 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics (the raw materialused is a mixture of PE, PP and PS) according to another example of thepresent invention.

FIG. 15 is a graph illustrating a change in gas production in a methodfor catalytically cracking waste plastics (the raw material used is amixture of PE, PP and PS) according to another example of the presentinvention.

FIG. 16 is a view illustrating yield of oil fraction of 90 minutesduration since waste plastics are loaded.

FIG. 17 is a graph illustrating a relationship between the oil fractionefflux time and the cumulative run-off quantity (weight %) in a methodfor catalytically cracking waste plastics (the raw material used is amixture of PP with PVC) according to another example of the presentinvention.

FIG. 18 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics (the raw materialused is a mixture of PP with PVC) according to another example of thepresent invention.

FIG. 19 is a graph illustrating a change in gas production in a methodfor catalytically cracking waste plastics (the raw material used is amixture of PP with PVC) according to another example of the presentinvention.

FIG. 20 is a graph illustrating a relationship between the oil fractionefflux time and the cumulative run-off quantity (weight %) in a methodfor catalytically cracking waste plastics (the raw material used is amixture of PP with PVC and a Ca compound to be added is changed to eachof CaO, CaCO₃ and Ca(OH)₂) according to another example of the presentinvention.

FIG. 21 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics (the raw materialis a mixture of PP with PVC and a Ca compound to be added is changed toeach of CaO, CaCO₃ and Ca(OH)₂) according to another example of thepresent invention.

FIG. 22 is a graph illustrating a change in gas production in a methodfor catalytically cracking waste plastics (the raw material is a mixtureof PP with PVC and a Ca compound to be added is changed to each of CaO,CaCO₃ and Ca(OH)₂) according to another example of the presentinvention.

FIG. 23 is a graph illustrating the XRD analysis result of calciumhydroxide in a method for catalytically cracking waste plastics (the rawmaterial is a mixture of PP with PVC and a Ca compound to be added ischanged to each of CaO, CaCO₃ and Ca(OH)₂) according to another exampleof the present invention.

FIG. 24 is a graph illustrating a relationship between the oil fractionefflux time and the cumulative run-off quantity (weight %) in a methodfor catalytically cracking waste plastics (in the coexistence of the FCCwaste catalyst (FCC(U)) with calcium hydroxide) according to anotherexample of the present invention.

FIG. 25 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics (in thecoexistence of the FCC waste catalyst (FCC(U)) with calcium hydroxide)according to another example of the present invention.

FIG. 26 is a graph illustrating a change in gas production in a methodfor catalytically cracking waste plastics (in the coexistence of the FCCwaste catalyst (FCC(U)) with calcium hydroxide) according to anotherexample of the present invention.

FIG. 27 is a graph illustrating the XRD analysis result ofFCC(U)-Ca(OH)₂ in a method for catalytically cracking waste plastics (inthe coexistence of the FCC waste catalyst (FCC(U)) with calciumhydroxide)according to another example of the present invention.

FIG. 28 is a graph illustrating the relationship between the oilfraction efflux time and the cumulative run-off quantity (weight %) in amethod for catalytically cracking waste plastics (the material is amixture of PP with PVC and a quantity of calcium hydroxide to be addedis changed at three different levels) according to another example ofthe present invention.

FIG. 29 is a graph illustrating a carbon number distribution of productsin a method for catalytically cracking waste plastics (the material is amixture of PP with PVC and a quantity of calcium hydroxide to be addedis changed at three different levels) according to another example ofthe present invention.

FIG. 30 is a graph illustrating a change in gas production in a methodfor catalytically cracking waste plastics (the material is a mixture ofPP with PVC and a quantity of calcium hydroxide to be added is changedat three different levels) according to another example of the presentinvention.

FIG. 31 is a schematic view briefly illustrating the apparatus ofreaction processes according to another example of the presentinvention.

FIG. 32 is a graph illustrating the material balance for the above case.

DESCRIPTION OF SYMBOLS

1: reaction vessel

2: heater

3: agitator

4: loading port for raw materials

5: cracked gas discharging port

6: cracked gas pipe

7: cooling mechanism

8: oil fraction storage tank

9: oil fraction (cracked oil)

10: cryogenic trap (−80° C.)

11: NaOH trap

12: GC-FID

13: discharge port

14: base

15: pivotally supporting portion

16: tilting device

21: rotary kiln-type reaction vessel

22: heater

22 a: combustor

24: loading port for raw materials

25: anterior fixing portion

25 a: raw material feeding mechanism

26: FCC waste catalyst and others inside reaction vessel

27: cooling mechanism

28: oil fraction storage tank

29: combustible gas (fuel gas)

30: posterior fixing portion

31: discharged substance storing portion

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an explanation will be made for the best mode for carryingout the present invention by referring to drawings. In description ofembodiments, waste catalyst (FCC waste catalyst) which is dischargedfrom petroleum refinery plants, is used as FCC catalyst.

EXAMPLES

The First Embodiment

FIG. 1 is a schematic view of an apparatus for catalytically crackingwaste plastics according to the first embodiment of the presentinvention.

In FIG. 1, the numeral 1 denotes a horizontal-type reaction vesselshaped in a cylindrical form and having a heater 2 as heating means anda rotary-vane type agitator 3 as agitating means. The heater 2 is usedto heat granular FCC waste catalysts loaded from a material port 4 up toa temperature range from 300° C. to 500° C., preferably from 400° C. to480° C. and more preferably from 410° C. to 430° C. In this embodiment,the heater 2 is such a heater that can be easily controlled fortemperatures, for example, an electric heater. Waste plastics which arefinely degraded into granules to flakes are loaded into granular FCCwaste catalysts heated to a high temperature inside the reaction vessel1 and mixed and agitated by the agitator 3 to dredge the waste plasticswith the high-temperature granular FCC waste catalysts, thereby allowingheating/decomposition reactions to proceed. In this embodiment, theagitator 3 is rotated at 50 rpm, thereby mixing and agitating the wasteplastics loaded from the material port 4 with the granular FCC wastecatalysts.

The numeral 5 denotes a cracked gas discharging port, and gas generatedby catalytically cracking of waste plastics is sent out from the crackedgas discharging port 5. The numeral 6 is a cracked gas pipe. In thisembodiment, cracked gas is sent out, with N₂ gas used as a carrier, andliquefied by a cooling mechanism 7 in which water and others is used asa refrigerant and available as an oil fraction (cracked oil). The thusobtained oil fraction (cracked oil) is stored at an oil fraction storagetank 8 and taken out as cracked oil 9.

N₂ gas is introduced into the reaction vessel 1 not only because it isused as a carrier gas for the cracked gas but also because oxygenconcentration inside the reaction vessel 1 is reduced. A rare gas suchas argon may be used in place of N₂ gas.

The numeral 10 denotes a cryogenic trap, which recovers an LPG fractionnot liquefied by the cooling mechanism 7 through a cryogenic trap (−80°C.) using dry ice. The numeral 11 denotes a NaOH trap, which is to traporganic matter produced by decomposition. The numeral 12 denotes GC-FID(gas chromatography-flame ionization detector), which is to make aquantitative analysis of low boiling-point substances such as methaneand ethane not liquefied by the cryogenic trap 10.

The numeral 13 denotes a discharge port formed at a lower part on oneend of the reaction vessel 1, 14 denotes a base for placing the reactionvessel 1 and the agitator 3, 15 denotes a pivotally supporting portionby which one end of the base 14 is pivotally supported, 16 is a tiltingdevice such as a pusher for elevating the other end of the base 14arranged at a lower part of the base 14 to tilt the base 14.

When the tilting device 16 is driven to tilt the base 14 and open adischarge port 13 to rotate the agitator 3, FCC waste catalysts anddecomposed residue are displaced axially toward the reaction vessel 1,and discharged from the discharge port 13. The tilting device 16 and theagitator 3 constitute a discharge mechanism in the present embodiment.

Since the discharge mechanism is provided, FCC waste catalysts andothers inside the reaction vessel 1 can be controlled to an appropriatelevel at which waste plastics can be loaded, thereby providing a stableoperation.

Hereinafter, the present invention will be explained more specificallyby referring to the following examples. The present invention shall notbe construed to be restricted to these embodiments. Also waste plasticssuch as polyethylene, polypropylene and others are respectivelyprocessed scrap of waste plastics.

(Experiment 1)

The catalytically cracking apparatus described in the first embodiment 1is used to carry out the following processes, namely, 10 g of granularFCC waste catalyst is heated to 420° C. by actuating a heater 2 inside areaction vessel 1, 75 g of granular to flake-shaped polyethylene (PE) isloaded into the high-temperature granular FCC waste catalyst from amaterial port 4, an agitator 3 is rotated at 50 rpm, the granular FCCwaste catalyst is mixed and agitated with granular to flake-shapedpolyethylene (PE), the polyethylene (PE) is dredged with thehigh-temperature granular FCC waste catalyst, thereby facilitatingheating/decomposition reactions. The decomposition reaction is set toproceed at 420° C. under an atmospheric pressure. Cracked gas is sentinto a cooling mechanism 7, with N₂ gas (100 mL/min) being used as acarrier, then, cooled and liquefied to obtain oil fractions.

FIG. 2 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products with (Example 1)or without the FCC waste catalyst (Comparative Example 1) whenpolyethylene (PE) is used as a raw material. Further, the reactiontemperature in Comparative Example 1 is elevated by 5° C. and to 425°C., as compared with the reaction temperature in Example 1 in place ofnot using the FCC waste catalyst.

As apparent from FIG. 2, the use of the FCC waste catalyst (FCC (U))results in a higher run-off speed and a slightly greater yield, despitethe fact that the reaction temperature is lowered by 5° C. Further, theuse of the FCC waste catalyst (FCC (U)) hardly produces wax or does notadversely affect the apparatus.

FIG. 3 shows a carbon number distribution of cracked oil. The carbonnumber distribution of cracked oil is determined by GC-FID.

As apparent from FIG. 3, the use of the FCC waste catalyst (FCC (U))results in a smaller molecular weight of products. This result is shownin Table 1 in terms of material balance. As indicated in Table 1,naphtha, kerosene and light oil fractions are increased to raise theutility value. Further, there is substantially no residue or nocarbonization found. Table 2 shows the structure of a product. Asapparent from Table 2, the use of the FCC waste catalyst (FCC(U))increases i-paraffin and aromatic compounds, producing various types ofproducts.

TABLE 1 Material balance FCC waste Free of catalyst catalyst [%] [%] Drygas (C1-C2) 1.5 2.9 LPG(C3-C4) 2.3 5.2 Naphtha (C5-C8) 2.7 21.5 Kerosene(C9-C12) 13.1 20.8 Light oil (C13-C24) 37.8 36.6 Heavy oil (C25-) 29.912.1 Coke 12.6 0.9 * The figure given in the column of catalyst-freecoke indicates a quantity of residue.

TABLE 2 Component ratio of products FCC waste Free of catalyst catalyst[%] [%] n-paraffin 60 11.0 Olefin 30 22.5 i-paraffin 0 11.5 Aromaticcompounds 1-2 45.0

(Experiment 2)

Evaluation is made for a relationship between the efflux time and thecumulative run-off quantity (weight %) of decomposition products, acarbon number distribution of cracked oil and a quantity of cracked gasproduced under the conditions the same as those in Experiment 1 exceptthat the reaction temperature is set at three levels, namely, 410° C.,420° C. and 430° C. It is noted that the cumulative run-off quantity(weight %) of decomposition products and the carbon number distributionof cracked oil are determined similarly as in Example 1.

FIG. 4 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products.

As apparent from FIG. 4, cracked oil is obtained at a higher yieldaccording to a higher reaction temperature, and the cracked oil flowsout at a greater speed. Further, as apparent from FIG. 6, gas isproduced at an increased quantity, and decomposition takes place moreeasily. However, as apparent from the carbon number distribution in FIG.5, compounds having a greater molecular weight increase in proportion toan increase in reaction temperature. This leads to an increased quantityof wax, which is not desirable. As described so far, a lower reactiontemperature results in a smaller quantity of wax but also results in alonger decomposition time to cause an increased quantity of residue. Incontrast, a higher reaction temperature results in a greater yield butmay result in an increased wax fraction and cause carbonization.Therefore, catalytic cracking to petroleum is preferable in which theFCC waste catalyst (FCC(U)) is used at a reaction temperature of 420° C.

(Experiment 3)

Evaluation is made for a relationship between the efflux time and thecumulative run-off quantity (weight %) of decomposition products, acarbon number distribution of cracked oil and a quantity of gas producedunder the conditions the same as those in Experiment 1 except that theFCC waste catalyst (FCC(U)) is set at three different quantities,namely, 5 g, 10 g and 20 g.

FIG. 7 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products. FIG. 8 shows acarbon number distribution of cracked oil. FIG. 9 shows a change in thequantity of gas production.

These results have revealed that when the FCC waste catalyst (FCC (U))is changed in quantity in a range from 5 g to 20 g, a quantity ofcracked oil is hardly changed but when the FCC waste catalyst (FCC(U))is in a quantity of 5 g, it undergoes decomposition for a longer time.Further, as apparent from FIG. 8, products are lower in molecular weightas the FCC waste catalyst (FCC (U)) is fed in an increased quantity.This finding may be due to the fact that an increased quantity of thecatalyst results in a larger area in contact with polyethylene (PE), araw material, thereby more easily causing the decomposition reaction. Itis likely that where the FCC waste catalyst (FCC(U)) is in a quantity of5 g, it undergoes a longer decomposition due to a smaller area incontact with the raw material and also results in greater molecularweight of products. On the basis of these findings, it is effective touse the FCC waste catalyst (FCC(U)) in a quantity exceeding 10 g,namely, 13 mass % or more with respect to the mass of waste plastics.

(Experiment 4)

Raw materials are subjected to catalytic cracking to petroleum under thesame conditions as those in Experiment 1 except that these raw materialsare polyethylene (PE), polypropylene (PP) and polystyrene (PS) at therespective quantities of 75 g.

FIG. 10 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products. FIG. 11 shows acarbon number distribution of cracked oil. FIG. 12 shows a change in gasproduction.

As apparent from FIG. 10, polypropylene (PP) and polystyrene (PS) can bedecomposed without a catalyst at a reaction temperature below 400° C.and therefore undergo decomposition all at once. However, polystyrene(PS) entails a great quantity of residue and resembles charcoal, fromwhich carbonization reaction has occurred. This finding may be due tothe fact that polystyrene (PS) is decomposed at a low temperature andsubstances responsible for carbonization are aromatic compounds,therefore, polystyrene (PS) having many benzene rings in structure issubjected to carbonization. In view of this finding, it is necessary tocarry out the reaction at a lower temperature in catalytically crackingpolystyrene (PS) alone to petroleum.

Further, as shown in FIG. 11, products are quite different incomposition due to a difference in structure of each raw material used.While polyethylene (PE) and polypropylene (PP) are distributed evenly,polystyrene (PS) mostly contains a carbon number of 8, which may be anaromatic compound easily removable from carbon chains. In contrast, asillustrated in FIG. 12, gas is produced at a greater quantity whenpolyethylene (PE) and polypropylene (PP) are used. This may be due tothe fact that polypropylene (PP) has many methyl groups in its structureto easily produce methane.

(Experiment 5)

Raw materials are subjected to catalytic cracking to petroleum under thesame conditions as those in Experiment 1 except that these raw materialsare a mixed material composed of 25 g of polyethylene (PE), 25 g ofpolypropylene (PP) and 25 g of polystyrene (PS), a total of 75 g.

FIG. 13 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products. FIG. 14 shows acarbon number distribution of cracked oil. FIG. 15 shows a change in gasproduction.

As apparent from FIG. 13, when the mixed material is used, a yield isdecreased as compared with a single raw material. Further, as apparentfrom FIG. 14, the carbon number distribution of products is greatlyinfluenced by polystyrene (PS) and polypropylene (PP), and flows out inthe order of easily decomposable substances (PS→PP→PE). Therefore,residual oil and residue are polyethylene (PE). Since polyethylene (PE)flows out as residual oil abundantly, it can be obtained at a greatyield by elevating the reaction temperature or increasing the quantityof the FCC waste catalyst (FCC (U)). Although the yield is notnecessarily great, polyethylene (PE)-abundant cracked oil which isobtained at a late stage of decomposition is also free of a waxfraction. Thus, the FCC waste catalyst (FCC (U)) is found effective andwaste plastics can be effectively decomposed to petroleum when the mixedmaterial is used.

(Experiment 6)

Oil fractions are collected under the same conditions as those inExperiment 1 except that 440 g of granular FCC waste catalyst is heatedto 420° C. by actuating a heater 2 inside a reaction vessel 1, and 75 gof granular or flake polyethylene (PE) is loaded into thishigh-temperature granular FCC waste catalyst from a material port 4,thereby allowing the decomposition reaction to proceed (Example 6).

Further, oil fractions are collected under the same conditions as thosein Example 6 except that in place of 440 g of the FCC waste catalyst, amixture of 500 g of sands with 10 g of the FCC waste catalyst (13 wt %with respect to waste plastics) is heated, to which 75 g of polyethylene(waste plastics) is added (Comparative Example 2).

Still further, oil fractions are collected under the same conditions asthose in Example 6 except that in place of 440 g of the FCC wastecatalyst, a mixture of 500 g of sands with 50 g of the FCC wastecatalyst (67 wt % with respect to waste plastics) is heated, to which 75g of polyethylene (waste plastics) is added (Comparative Example 3).

Table 3 is a list showing a mass (g) of cracked oil and LPG fraction anda yield(%) of oil fractions obtained for 95 minutes after waste plasticsare loaded. FIG. 16 is a graph showing the yield of oil fractionsobtained for 90 minutes after waste plastics are loaded. It is notedthat the yield of oil fractions is expressed by (mass of crackedoil+mass of LPG fraction)/(mass of waste plastics)×100(%).

TABLE 3 Catalyst Sand Cracked oil LPG fraction Oil yield (g) (g) (g) (g)(%) Example 6 440 0 45.0 17.4 83.2 Comparative 10 500 13.0 4.3 23.1Example 2 Comparative 50 500 20.1 7.3 36.5 Example 3

It is apparent from Table 3 and FIG. 16 that in Example 6, oil fractionsare collected at a greater quantity as compared with ComparativeExamples 2 and 3 where sands are used as thermal vehicle, and a yield of80% is attained in 90 minutes.

It is apparent that oil fractions are obtained at a higher yieldaccording to the present Example, as compared with a case disclosed inPatent Document 1 where sands are used to heat and decompose wasteplastics.

(Experiment 7)

Raw materials are subjected to catalytic cracking to petroleum under thesame conditions as those in Experiment 1 except that the raw material isa mixed material composed of 67.5 g of polypropylene(PP) and 7.5 g ofpolyvinylchloride(PVC).

FIG. 17 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products in cases where araw material composed of polypropylene (PP) alone is decomposed at 425°C. without using the FCC waste catalyst (Comparative Example 4), where amixture of polypropylene (PP) with polyvinyl chloride (PVC) isdecomposed at 425° C. without using the FCC waste catalyst (ComparativeExample 5) and where a mixture of polypropylene (PP) with polyvinylchloride (PVC) is decomposed at 420° C. by using the FCC waste catalyst(Example 7). FIG. 18 shows a carbon number distribution of cracked oil.FIG. 19 shows a change in gas production.

These results have revealed that chlorine content in the structure ofwaste plastics, which is a raw material, is mostly converted intohydrogen chloride. Further, a yield is found to decrease when polyvinylchloride (PVC) is present in a raw material. It has also been confirmedthat a charcoal-like solid substance remains inside a reaction vessel 1,coming out in a mixture with cracked oil during the reaction. Thecharcoal-like solid substance mixed with cracked oil can be removed bymeans such as percolation and others. This finding makes it possible toobtain clean cracked oil. Still further, since the volume is changed by60% as compared with Comparative Example 4 where no PVC is mixed, PVCmay easily undergo carbonization, which is likely to affect the yield.However, the use of the FCC waste catalyst (FCC(U)) makes it possible toreduce quantities of residual oil and residue, thereby facilitating thedecomposition and effectively preventing the occurrence of carbonizationwhen waste plastics mixed with polyvinyl chloride (PVC) are used.

In contrast, as shown in FIG. 18, the use of the FCC waste catalyst (FCC(U)) makes the carbon number distribution of products even. This findingis due to a difference in the reaction mechanism. The carbon numeral 8is found to be disproportionately distributed in the radical chainreaction (free of catalyst). When the FCC waste catalyst (FCC(U)) isused, ion reaction may take place to result in various types ofproducts. As shown in FIG. 19, the use of the FCC waste catalyst(FCC(U)) produces a great quantity of gas at one point. In principle,since polypropylene (PP) can be easily decomposed even without catalystsat a temperature below 400° C., it is likely that polypropyleneundergoes the reaction all at once as a result of accelerateddecomposition by the FCC waste catalyst (FCC(U)), thereby generating agreat quantity of gas. This fact can be estimated by referring to agreater run-off quantity at the time of starting the flow.

It has also been confirmed that no dioxin is generated inside thereaction vessel, which is due to a decreased oxygen concentration insidethe reaction vessel for decomposing and gasifying polyvinyl chloride(PVC) by introduction of N₂ gas into the reaction vessel.

(Experiment 8)

Raw materials are subjected to catalytic cracking to petroleum under thesame conditions as those in Example 1 except that for the purpose ofremoving hydrogen chloride, calcium oxide (CaO), calcium carbonate(CaCO₃) and calcium hydroxide (Ca(OH)₂) are separately used at therespective quantities of 7.5 g to give a mixed raw material comprising67.5 g of polypropylene (PP) and 7.5 g of polyvinyl chloride (PVC).

FIG. 20 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products in cases where amixture of polypropylene (PP) with polyvinyl chloride (PVC) isdecomposed at 420° C. without mixing the FCC waste catalyst but byadding calcium oxide, where a mixture of polypropylene (PP) withpolyvinyl chloride (PVC) is decomposed at 420° C. without mixing the FCCwaste catalyst but by adding calcium carbonate and where a mixture ofpolypropylene (PP) with polyvinyl chloride (PVC) is decomposed at 420°C. without mixing the FCC waste catalyst but by adding calciumhydroxide. FIG. 21 shows a carbon number distribution of cracked oil.FIG. 22 shows a change in gas production. FIG. 23 shows the result ofXRD analysis of calcium hydroxide after catalytic cracking to petroleum.

As apparent from FIG. 20, where calcium carbonate is used, no influenceis found on the yield, depending on a difference in Ca compounds,although the run-off speed is low. Determination of chlorine content incracked oil by using a simple detector tube method has revealed adifference in a quantity of chlorine due to Ca compounds. Of Cacompounds, calcium hydroxide is found most efficient in effecting theremoval. Although calcium hydroxide is the lowest in mol number on molconversion even at the same quantity of 7.5 g, it is able to removesubstantially all hydrogen chloride generated, and the chlorine portioncontained in cracked oil is about half when compared with that in theother two compounds. Calcium hydroxide is found to most easily reactwith hydrogen chloride. As indicated in FIG. 23 on the XRD analysis,calcium hydroxide is given as CaClOH. Other peaks have a crystallinestructure of CaCl₂, in which it is likely that one hydroxyl group ofcalcium hydroxide is at first substituted and another hydroxyl group isthen substituted and thereafter, still another hydroxyl group is allowedto react, or a two-stage reaction is conducted to remove hydrogenchloride.Ca(OH)₂+HCl→CaClOH+H₂OCaClOH+HCl→CaCl₂+H₂O  [Chemical formula 2]

As shown in FIG. 21, Ca compounds hardly influence products and calciumhydroxide gives a similar distribution as with the other two compounds.Since there is no change in yield or carbon number distribution ofproducts, calcium hydroxide exhibiting the highest efficiency ofremoving hydrogen chloride is preferably used in decomposition ofplastics including chlorine content.

(Experiment 9)

Evaluation is made for the influence of coexistence of calcium hydroxideused in removing hydrogen chloride with the FCC waste catalyst (FCC(U)). A mixture of 67.5 g of polypropylene (PP) with 7.5 g of polyvinylchloride (PVC), as a subject to be catalytically cracked to petroleum,is mixed and agitated in the same reaction field as 10 g of the FCCwaste catalyst (FCC (U)) and 7.5 g of calcium hydroxide (Ca(OH)₂),thereby facilitating the reaction and decomposition to petroleum. Otherconditions are the same as those described in Example 1.

FIG. 24 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products in cases where amixture of polypropylene (PP) with polyvinyl chloride (PVC) isdecomposed at 420° C. in the presence of the FCC waste catalyst (Example9), where a mixture of polypropylene (PP) with polyvinyl chloride (PVC)is decomposed at 420° C. without mixing the FCC waste catalyst but inthe presence of calcium hydroxide (Comparative Example 6) and where amixture of polypropylene (PP) with polyvinyl chloride (PVC) isdecomposed at 420° C. in the presence of the FCC waste catalyst andcalcium hydroxide (Example 10). FIG. 25 shows a carbon numberdistribution of cracked oil. FIG. 26 shows a change in gas production.FIG. 27 shows the result of XRD analysis of a mixture of the FCC wastecatalyst with calcium hydroxide after catalytic cracking to petroleum.

As apparent from FIG. 24, coexistence of the FCC waste catalyst (FCC(U)) with calcium hydroxide results in a slow run-off speed and a lowyield, thereby making decomposition of waste plastics difficult. Thisfinding may be due to the fact that calcium hydroxide reacts withhydrogen chloride to produce water but the water acts as a catalystpoison of FCC (U). Despite the above finding, in view of an efficientremoval of chlorine, coexistence of the FCC waste catalyst (FCC (U))with calcium hydroxide is preferable to a single use of calciumhydroxide.

Further, as illustrated in FIG. 27, as with XRD found in a single use ofcalcium hydroxide, CaClOH has been produced in a mixture of the FCCwaste catalyst with calcium hydroxide after catalytic cracking topetroleum, which is suggestive of the occurrence of a similar reaction.Still further, as illustrated in FIG. 25 and FIG. 26, a carbon numberdistribution of products in the coexistence of the FCC waste catalyst(FCC (U)) with calcium hydroxide is similar to that found in a singleuse of the FCC waste catalyst (FCC (U)). A gas production quantity inthe coexistence of the FCC waste catalyst (FCC (U)) with calciumhydroxide is similar to that found in a single use of calcium hydroxide.On the basis of these findings, such favorable results are obtained thatproducts are available in a wide variety and gas is produced in asmaller quantity. As illustrated in FIG. 24, since a gradient indicatingthe yield of cracked oil is kept unchanged at a late stage of thereaction time, the yield is considered to become greater as the reactiontime is extended. Therefore, a reaction process in the coexistence ofthe FCC waste catalyst (FCC (U)) with calcium hydroxide is effective andalso practical.

(Experiment 10)

Evaluation is made for an optimal quantity of calcium hydroxide whenwaste plastics in which plastics having a chlorine atom as acomposition, such as polyvinyl chloride (PVC), are mixed are subjectedto catalytic cracking to petroleum. Waste plastics (a raw material)which is a mixture of 67.5 g of polypropylene (PP) with 7.5 g ofpolyvinyl chloride (PVC), are prepared by incorporating 10 g of FCCwaste catalyst (FCC (U)) and calcium hydroxide (Ca(OH)₂) at threedifferent quantities of 2 g, 5 g and 7.5 g. The raw material, FCC wastecatalyst (FCC (U)) and calcium hydroxide are then mixed and agitated inthe same reaction field, thereby facilitating the reaction anddecomposition to petroleum at 420° C. Other conditions are the same asthose described in Experiment 1.

FIG. 28 shows a relationship between the efflux time and the cumulativerun-off quantity (weight %) of decomposition products. FIG. 29 shows acarbon number distribution of cracked oil. FIG. 30 shows a change in gasproduction.

As apparent from FIG. 28, reactions will take place more easily ascalcium hydroxide (Ca(OH)₂) is decreased in quantity. This finding showsthat water acts as a catalyst poison to decrease the decompositionefficiency of waste plastics. The result of chlorine analysis of crackedoil has revealed that when calcium hydroxide (Ca(OH)₂) is available in aquantity of 5 g corresponding to approximately half of the chlorinecontent in the raw material, the greatest removal efficiency is obtainedand substantially all calcium hydroxide reacts with chlorine. Asillustrated in FIG. 29 and FIG. 30, there is substantially no differencein the carbon number distribution of products, and a gas production isincreased in the order of easily decomposable substances. Further, aquantity of calcium hydroxide does not influence the carbonization.Therefore, it has been confirmed that chlorine-containing waste plasticsare effectively decomposed by using calcium hydroxide (Ca(OH)₂) havingthe mol number which is approximately half the chlorine contentcontained in a raw material.

The results of Experiment 1 through 10 are summarized in Table 4. Inthis Table 4, a circle given in the column of FCC waste catalystindicates a case where the FCC waste catalyst is used and a crossindicates a case that the catalyst is not used. Further, a cross givenin the column of Ca compounds indicates a case where no Ca compound isused, and the column where any Ca compound is shown indicates a casewhere the Ca compound is used.

As apparent from Table 4, when calcium hydroxide (Ca(OH)₂) is used as aCa compound generating hydrogen chloride and chlorine in cracked oil arekept to an extremely low level. Among other things, the best result isobtained in a combined use of the FCC waste catalyst with calciumhydroxide (Ca(OH)₂).

TABLE 4 Result of quantitative determination of chlorine content FCCGenerated Chlorine in cracked oil waste catalyst Ca compounds HCl [mmol][mmol] [ppm] X X 98.0 1.75 1150 ◯ X 74.0 1.27 830 X CaCO₃ 76.0 0.736 480X CaO 17.0 0.655 433 X Ca(OH)₂ 0.60 0.324 210 ◯ Ca(OH)₂ 0.42 0.159 118Cl: 112 mmol

(Experiment 11)

A raw material (RDF composed of PE, PP, PS, chlorine content of 1.4% andash of 4.4% (solid fuel)) illustrated in Table 5 is processed by arotary kiln-type (rotary drum-type) reaction vessel rotating at 50 rpmand a carrier gas N₂ is blown therein from two sites under a reactionpressure of 1 atm at a quantity of 50 mL/min. Waste plastics aresubjected to catalytic cracking to petroleum at reaction temperaturesand mixture ratios of raw material with a catalyst given in Table 5 (theupper level).

Table 6 (middle level) shows a material balance of products obtainedafter the reaction of catalytically cracking waste plastics topetroleum. Further, Table 6 (lower level) shows coke (in catalyst)[wt%], quantity of generated hydrogen chloride [mmol] and chlorine contentin cracked oil [ppm].

TABLE 5 <Cracking conditions> Raw material RDF (PE 44%, PP 36%, PS 15%,chlorine content 1.4%, ash 4.4%) Reaction pressure 1 atm Agitation speed50 rpm Flow rate of carrier gas 100 ml/min (50 ml/min × 2)

TABLE 6 <Cracking results> Free of 1) 2) 3) catalyst FCC(U) Ca(OH)₂ Ironore Fe₂O₃ FeOOH Reaction temperature [° C.] 435 420 435 435 435 435 Rawmaterial load 266.6 1109.9 267.4 511.1 377.7 366.6 quantity [g] FCC(U)[g] 1367.37 970.16 1021.47 1009.04 976.08 Ca(OH)₂ [g] (30% of 247.93160.64 180.7 164.3 FCC) Fe compound [g] (10% of 208.32 100.0 110.7 FCC)Quantity of catalyst [g] 1367.4 1218.1 1390.4 1289.7 1251.1 Cracked oil[wt %] 60.6 64.9 64.5 48.2 44.7 50.8 LPG fraction [wt %] 3.4 13.6 12.711.1 15.6 14.7 Methane [wt %] 2.5 7.2 5.4 2.9 4.3 6.4 Residue [wt %]19.8 10 — 16.7 33.3 23.1 Material balance [%] 86.3 95.7 82.6 78.9 97.995.0 Coke (in catalyst) [wt %] — — — — — — Generated hydrogen 51 165 0 00 0 chloride [mmol] Chlorine content in 1258 680 120 85 139 74 crackedoil [ppm]

As shown in Table 6 (upper level), in this Example, when iron hydroxide(III)-rich iron ore is mixed as an iron compound at 20 mass % withrespect to FCC (U), a quantity of generated hydrogen chloride is 0[mmol] and a quantity of chlorine content in cracked oil is 85 [ppm]which is lower than the TR criteria (Technical Report criteria) of 100[ppm] as shown in Table 6 (lower level).

Further, where Fe₂O₃ is mixed as an iron compound at 10 mass % withrespect to FCC(U), as shown in Table 6 (lower level), a quantity ofgenerated hydrogen chloride is 0 [mmol], and chlorine content in crackedoil is 139 [ppm], which exceeds the TR criteria (Technical Reportcriteria) of 100 [ppm]. However, the level is still low.

Still further, where iron hydroxide (III) (FeO(OH)) is mixed as an ironcompound at 11 mass % with respect to FCC(U), as shown in Table 6 (lowerlevel), a quantity of generated hydrogen chloride is 0 [mmol], andchlorine content in cracked oil is 74 [ppm], which is greatly lower thanthe TR criteria (Technical Report criteria) of 100 [ppm].

The Second Embodiment

FIG. 31 is a schematic view of an apparatus for catalytically crackingwaste plastics according to the second embodiment of the presentinvention.

In FIG. 31, the numeral 21 denotes a reaction vessel or a rotarykiln-type (rotary drum-type) of a reaction vessel. The numeral 22denotes a heater as heating means. As illustrated in FIG. 31, in acombustor 22 a of this Embodiment, fuel and air are mixed and burnt toheat a catalyst and others 26 inside the reaction vessel 21 from thebottom of the reaction vessel 21. The numeral 24 denotes a loading portfor raw materials, functioning to load waste plastics (a raw material),the FCC waste catalyst (FCC(U)), Ca compounds such as calcium hydroxideand iron oxide into the reaction vessel 21. The numeral 25 denotes ananterior fixing portion to place and fix a raw material feedingmechanism 25 a composed of a conveyor for loading raw materials andwaste catalysts. The numeral 27 denotes a cooling mechanism which is inassociation with an inert gas such as nitrogen gas and rare gas, therebycooling cracked gas from the rotary kiln-type (rotary drum-type)reaction vessel 21 to liquefy and storing the thus liquefied gas at anoil fraction storage tank 28. The numeral 29 denotes a combustible gaswhich is not liquefied (fusel gas). The numeral 30 denotes a posteriorfixing portion, which is in contact with an opening at the back of therotary kiln-type (rotary drum-type) reaction vessel 21 and by whichwaste plastics loaded one after another are decomposed and gasified todischarge cracked gas continuously, and the FCC waste catalyst, Cacompounds, decomposed residue and the like are discharged intermittentlyat a time when a predetermined quantity of waste plastics is completelydecomposed and gasified. The numeral 31 denotes a discharged substancestoring portion for storing the FCC waste catalyst, Ca compounds anddecomposed residue discharged from the reaction vessel 21.

In this Embodiment, the FCC waste catalyst (FCC(U)), calcium hydroxide(Ca compound), iron compounds and waste plastics (raw material) insidethe rotary kiln-type (rotary drum-type) reaction vessel 21 are mixed andagitated by rotation of the rotary kiln-type (rotary drum-type) reactionvessel 21, thereby allowing catalytically cracking reaction to proceed.The catalytically cracking of waste plastics to petroleum and thereaction mechanism of trapping hydrogen chloride by Ca compounds aresimilar to those described in the previous Examples.

The FCC waste catalyst and the like discharged into the dischargedsubstance storing portion 31 are separated from decomposed residue onthe basis of a difference in specific gravity or by using a sieve,remaining portions are washed, thereby dissolving water-soluble calciumchloride in water to take out the FCC waste catalyst, Ca compounds andiron compounds prior to reaction. The thus taken out FCC waste catalyst,Ca compounds and iron compounds are regenerated, whenever necessary,after being dried. They can be then reused by addition of Ca compounds.The concentration of calcium chloride in drain water after the FCC wastecatalyst is washed is determined to calculate a quantity of Ca compoundsused in a dechlorination reaction, and the thus calculated quantity isadded accordingly.

FIG. 32 shows a material balance in this Embodiment. It is apparent fromthis drawing that an oil fraction can be obtained at a high yield of90%.

The present invention relates to a method for thermally decomposingwaste plastics, namely, waste materials of plastics such as polyethylene(PE), polypropylene (PP), polystyrene (PS) or polyethylene terephthalate(PET) and waste plastics having a resin, for example, polyvinyl chloride(PVC), in which chlorine is contained as a composition, and an apparatustherefor, and the present invention can provide a method forcatalytically cracking waste plastics which is excellent indecomposition reaction efficiency, capable of decomposing polyethylenecomposed of linear chain molecules which is difficult in decompositionat a low temperature, with a negligible quantity of decomposed residue,simple in process and able to realize a high energy efficiency of 50% ormore in terms of net yield of oil fraction, and a catalytically crackingapparatus.

1. A method for catalytically decomposing solid waste plasticscomprising: externally heating a horizontal-type reaction vessel, formedto a cylindrical shape, and containing a mixture of a granular FCC wastecatalyst and a granular Ca compound, the mixture thereby beingpreliminary heated to a temperature range from 350° C. to 435° C.,wherein the amount of the FCC waste catalyst is 20 to 60 vol% of thecapacity of the reaction vessel, and the Ca compound is present in anamount of 15 to 50 parts by mass with respect to 100 parts by mass ofthe FCC waste catalyst, adding and mixing/agitating granular orflake-shaped solid waste plastics by the agitator into the mixture ofthe heated granular FCC waste catalyst and the Ca compound and allowingthe solid waste plastics to be in direct contact with the mixture at atemperature range from 350° C. to 435° C., processing the solid wasteplastics inside the reaction vessel at a flow rate of 0.2 g to 10 g ofthe solid waste plastics per gram of the catalyst per hour and heatingwhile coating the heated granular FCC waste catalyst onto the surface ofthe solid waste plastics to cause decomposition and gasification of thesolid waste plastics via an ion reaction, and producing gaseoushydrocarbons, and removing the gaseous hydrocarbons from the reactionvessel by a carrier gas.
 2. A method for catalytically decomposing solidwaste plastics according to claim 1 wherein the energy efficiencyexpressed as net yield of the gaseous hydrocarbons is 50% or more,wherein the resulting hydrocarbons contain aromatized products, branchedhydrocarbon, and linear chain hydrocarbon, wherein the total amount ofthe aromatized products and the branched hydrocarbon is greater thanthat of the linear chain hydrocarbon; and wherein the resultinghydrocarbons contain chlorine in an amount of 139 ppm or less.
 3. Amethod for catalytically decomposing solid waste plastics according toclaim 2, wherein the Ca compound is Ca(OH)₂, CaCO₃, or CaO.
 4. A methodfor catalytically decomposing solid waste plastics according to claim 3further comprising: mixing granular iron compounds with the FCC wastecatalyst.
 5. A method for catalytically decomposing solid waste plasticsaccording to claim 4 wherein the granular iron compounds are ironhydroxide (III) (FeO(OH)).
 6. A method for catalytically decomposingsolid waste plastics according to claim 5, wherein the reaction vesselis a rotary kiln-type reaction vessel and further comprising: loadingthe waste plastics continuously to effect decomposition andgasification.
 7. A method for catalytically decomposing solid wasteplastics according to claim 2, wherein the reaction vessel is a rotarykiln-type reaction vessel and further comprising: loading the wasteplastics continuously to effect decomposition and gasification.
 8. Amethod for catalytically decomposing solid waste plastics according toclaim 3, wherein the reaction vessel is a rotary kiln-type reactionvessel and further comprising: loading the waste plastics continuouslyto effect decomposition and gasification.
 9. A method for catalyticallydecomposing solid waste plastics according to claim 4, wherein thereaction vessel is a rotary kiln-type reaction vessel and furthercomprising: loading the waste plastics continuously to effectdecomposition and gasification.
 10. A method for catalyticallydecomposing solid waste plastics according to claim 1 furthercomprising: mixing granular iron compounds with the FCC waste catalyst.11. A method for catalytically decomposing solid waste plasticsaccording to claim 10 wherein the granular iron compounds are ironhydroxide (III) (FeO(OH)).
 12. A method for catalytically decomposingsolid waste plastics according to claim 11, wherein the reaction vesselis a rotary kiln-type reaction vessel and further comprising: loadingthe waste plastics continuously to effect decomposition andgasification.
 13. A method for catalytically decomposing solid wasteplastics according to claim 10, wherein the reaction vessel is a rotarykiln-type reaction vessel and further comprising: loading the wasteplastics continuously to effect decomposition and gasification.
 14. Amethod for catalytically decomposing solid waste plastics according toclaim 1, wherein the reaction vessel is a rotary kiln-type reactionvessel and further comprising: loading the waste plastics continuouslyto effect decomposition and gasification.